Core of comminuted magnetic material



Oct. 22, 1940.

A. D. WHEPPLE I CORE 0F COMMINUTED MAGNETIC MATERIAL Filed April 25,1938 3 Sheets-Sheet 1 HIL 1|||| llTli l I! u INVENTOR.

4L1. EN. 0 WH/PPLE ATTORNEY.

Oct. 22, 1940. D HEPPL 2,218,669

001K8 0 COMNINUTED MAGNETIC MATERIAL Filed April 25, 1938 3 Sheets-Sheet2 INVENTOR.

AQLENQ WH/PPLE.

ATTORNEY.

06L 1940' A. D. WHIPPLE CORE CF CQMHINUTED MAGNETIC MATERIAL Filed April25, 1938 3 Sheets-Sheet 3 INVENTOR. 41. LEN D WH/PPLE ATTORNEY.

. not correspondingly increased, due to the mag- Patented Oct. 2 2, 1940I PATENT OFFICE 2,218,669 cone or 'oommmmn MAGNETIC Allen D. Whipple,Alexandria, Ind., minor to Johnson Laboratories, Inc'., Chicago, 111., aco;-

poration of Illinois Application April 25, 1938, Serial No. 204,245

3Claims.

My invention relates to an improved form of core consisting ofcompressed comminuted magnetic material by which the core is providedwith connection members adapted to facilitate the movement of the corelongitudinally by flexible operating means, such for example as flexiblecables. for use in connection with inductance coils respectivelyassociated with the cores, so that the effective permeability of themagnetic paths of the coils may be changed as desired by movement of thecores to correspondingly change the inductance of the coils for tuningand other purposes.

Commercial developments in the art of radio communication havedemonstrated the advantages of incorporating cores of the class referredto, in radio transmitting and receiving apparatus, for example, invariable inductance units forming parts of high frequency resonantcircuits for tuning purposes. The relatively low inductance of thematerial of the cores, greatly increases the effective permeability ofthe magnetic paths of the inductance coils with which the cores areused, with a corresponding increase in the inductance of said coils forany condition for which the cores constitute effective parts of themagnetic paths of the coils; the effective resistances of the circuitswith which the cores are used, are

netic particles of the cores beingof minute size and being electricallyinsulated from each other notwithstanding the many tons of pressureexerted upon said particles to compress them into stable solidifiedmagnetic cores; in such inductance tuned resonant circuits, thecapacitors required to selectively tune the circuits over a desiredrange of frequencies, are of fixed capacitance and are of small size;besides being relatively stable in use; as a result, such variableinductance tuning units may be compact and of consideration haverequired, heretofore, forms of operating mechanism so exact, expensiveand Cores of the kind described are adapted comminuted magnetic materialare operated by even complicated in some cases, for example, where gangoperation of a plurality of the cores has been required, as tosubstantially offsetv said advantages from the economical standpoint.Cores of the kind referred to, although they have 15 substantially thesame appearance as cores of solid soft iron, are in fact weak undermechanical strain, so brittle that they cannot be bent or deformed toany appreciable degree without rup-- ture, and so easily injured bytooling operations on account of the soft nature of the particles of thecores and the burnishing effects of the tools on the cores, that turningthe cores or otherwise machining them, is apt to produce continuous .andelectrically conductive metal paths on the 15 machined surfaces, whichfor the higher frequencies of operation for which the cores areintended, serve to impede the magneticv operation of the cores, and to adegree oifset some of the advantages they would otherwise have. As aresult, it is practically necessary that the cores be completelyfinished when they leave the molds in which they are compressed, andfurthermore in making the compressed cores, it is of the greatestimportance to avoid undue burnishing eifects between the compressedcores and the molds in ejecting them from the molds, to make certainthat electrically conductive paths of metal are not produced around thecores.

From the nature of the cores above referred to, it develops thatattempts to operate themin variable inductance tuning units, by means ofrigid mechanical operating structures, either recomminuted magneticmaterial, are obviated by a recently proposed type of variableinductance tuning unit, in which the cores of compressed flexible cablesconnected with the ends of the cores and extending to suitable operatingdevices by which the cores may be accurately operated without developingappreciable transverse strains in them, and by which they may be simplyand successfully arranged for gang operation if desired. The coresconstituting the subject matter of my present invention, which may haveany form of cross-section and any proportions desired, are particularlyadapted for use in variable inductimce tuning devices of the kind lastreferred to, and particularly where it is desired to use such coreshaving great length relatively to their diameter. On account ofthedim'culty of ejecting long slender cores of compressed comminutedmagnetic material-from the molds, it has hereto fore been diflicult ifnot impossible to produce such'cores satisfactorily, exceptingby meansof the improved devices disclosed in my co-pending application SerialNo. 196,653, which I find very satisfactory in producing such cores withlengths of from eight to ten times the diameter of the core and withoutappreciable burnishing, and with no harmful results of any kind from theejection of the cores from the molds in which they are compressed, thecores being true, and not deformed in anyway when they are ejected fromthe molds.

By my present invention, I am able to provide long slender cores ofcomminuted magnetic material with end connection members which, eventhat the amount of metallic material involved shall be no more thanrequired to reliably withstand the operating forces which maybe exertedon the cores by the flexible cables when the coresv are in use; thisresults in a form or forms oi connection members which are readilydeformable under the great pressures involved in compressing thecomminuted magnetic material to form the cores, unless specialprovisions are employed to prevent such deformation. It is one of theobjects of my invention to provide improved-apparatus for supporting theconnection members during the compression of the cores, sothat' suchdeformation of the external parts of the connection member will notoccur during the compression of the cores, and in addition, my presentinvention includes the improved process of making the cores of the kindreferred to, with connection members of kinds susceptible to readydeformation during compression but so manipulateddur- 01' a compressingoperation,

75' Fig. 3 shows in a view similar to Fig.

ing'the making of the cores that deformation of the external parts ofthe connection member does not occur. i

My invention will be best understood by reference to the accompanyingdrawings illustrating a preferred embodiment thereof, in which a Fig. 1illustrates in vertical; central, sectional view, and somewhatschematically, a form of machine in accordance with my said co-pendingapplication and adapted to produce long slender cores in accordance withmy present invention,

Fig. 2 shows in a view similar to Fig. 1, the mold portion of themachine, with the compressing plunger in its position assumed at thebeginning 2, the

compressing plunger operation,

Fig. 4 shows in side elevation and to an enlarged scale, the lower endof the compressing plunger,

' Fig. 5 is a vertical, sectional view through the compressing plunger,taken along theline 5-5 in Fig. i,

Fig. 6' shows in front elevation, a thin insert plate used in the end ofthe compressing plunger showninFigsAandd Fig.- 7 is an end view of theplate shown in Fig. 6,

, Figs. 8, 10; l2'and 14, show respectively different forms oiconnection members that may be employed in connection with my presentinvention,

Figs. 9, 11, 13 and 15 are side views of the connection membersrespectively illustrated in Figs. 8, 10, 12 and 14,

Figs. 16, 1'1, 18 and 20 are respectively plan views of completed coresequipped respectively at the end of a compressingwith connection membersof the kinds illustrated in Figs. 8, 10, 12 and 14, Y

Fig. 19 is a front elevation illustrating the core shown in Fig. 1'7, aswell as the core shown in Fig. 18, since said front elevation is thesame for eitherof the said cores, and

Fig. 21 shows in front elevation the core illustrated in Fig. 20. ,r

Similar numerals refer .to similar parts throughout the-several views. p

The core machineillustrated in Fig; 1 includes a base Hi having atubular bore in which a tubular and floating cell i l is disposed foraxial move.- ment, the cell I i being held in its position nearest thecompressing plunger I 2 by a spring it which has suflicient strength tosupport the floating cell but insumcient strength to in any wayinterfere with free movement of the cell during a compressing operationMovement of the cell it under the action of the spring it is limited bya tubular housing it surrounding the spring it and supported by the baseit. The cell H contains a bore l5 which is tapered slightly with itslarger end towards the compressing plunger l2, and the mold it of themachine is correspondingly externally tapered and fits the bore I5. The

mold it is provided with a bore Eta of the size of the cores to be madeby the machine, and said mold is divided into a plurality of sectionslongitudinally of the mold, so that raising the mold relatively to thecell I 9- permits a slight radial expansion of the mold sections, whichfrees the compressed core for ready ejection without appreciableburnishing of the core and without distorting the core in any way fromthe form imparted to it by the mold it. The small movement of the moldit towards the compressing plunger 82, to free a compressed core, islimited by a plate i? carried by the cell ii As a result of theconstruction described, after a core is compressed in the mold lit-andthe compressing plunger i2 is withdrawn, movement of the ejectingplunger 218 into the mold, easily removes the compressed core-because ofthe housing it limiting movement of the cell H, and also because of theplate i limiting movement of the mold It, the adhesive forces betweenthe mold and the compressed core being practically eliminated by theexpansion of the mold it. The plungers l2 and H8 may be operated by anyknown means, not

shown.

By means of this machine, able to produce accurate cores or comminutedimproved cores of my present invention, in the first place, the bodyportion of the plunger l2, which includes a body portion and a bushinglib for butting engagement with said body portion but not mechanicallyconnected therewith, is raised sufficiently to permit a charge IQ ofcomminuted magnetic material to be placed in the mold IS, the bushingl8b of the ejecting plunger l8 being in the, lower end of the mold, inwhich position it is held positively by the body portion of the plungerl8 during the compressing operation. The bushings I2!) and lib, whichare similar, carry in the manner described below, connection members 20and M respectively, which have projecting end portions extending towardsthe cavity in the mold l6. After a charge l9 has been placed in themold, the bushing Rb and the connection member 20 carried thereby areplaced in the mold and the compressing plunger l2 is forced into themold by any suitable means not shown until the charge I! is compressedfrom a condition illustrated in, Fig. 2 to the compressed conditionillustrated at l8a in Fig. 3. Dining this operation, the projectingportions of the connection members 20 and II are forced into thecomminuted material before it is appreciably compressed and aresubjected to the compressive forces developed in said material by theplunger l2, the result being that the projecting end portions of theconnection, members are deformed from the shape illustrated in Fig. 2 tothe shape illustrated at Illa and 2la in Fig. 3, thereby effecting aclinching engagement of the connection members with the material of thecompressed oore.

During the compressing operation, the spring I! permits the cell II tomove more or less with the compressing plunger l2, depending upon howthe intermediate adhesions develop between the material being compressedin the mold and the surface of the mold, which effects a substantiallyhomogeneous distribution of the compressive pressures throughout thematerial in the mold. The pressure forcing the mold l8 into the cell H,is at all times substantially equal to the force of the spring I3 uponthe cell H, which results in later requiring correspondingly smallpressure during ejection, to release the mold for expansion. After thecompression of the charge is ended, the body portion of the plunger [2is raised by suitable means not shown and the ejecting plunger I8 ismoved into the mold, and by its initial movement due to the largeadhesions or friction then existing between the compressed charge andthe mold, the mold I6 is moved a small distance with the plunger. IS, inthe cell ll, assuming that the cell is at the time in engagement withthe housing I, and if it is not in such engagement,

the movement of the mold l6 relatively to the I cell ll just described,is efiected immediately 78 moves thesolidifled core Ila and the adheringbushings lib and Ill; from the mold, and the machine is ready for themaking of the next core, after the ejecting plunger l8 has beenretracted and thelmold l6 has been firmly seated in the cell H.

- To support the connection members during the compressing operation,thebushings i217 and I8?) are constructed as illustrated for the bushingl2b in Figs. 4 and 5. It will be understood that to stand the largecompression pressures exerted upon the charge of comminuted magneticmaterial tocompress it into a solidified core, which pressuresfrequently amount to many tons, the

bushings must be constructed of a metal which is highly resistant todeformation, for example, hardened steel or steel alloy of one kind oranother, and that as a result it is diflicult to tool the compressingfaces of the bushings to provide proper seats in them for the connectionmembers, particularly where, as in the present case, the connectionmembers are made of thin material to reduce to a minimum the amount ofmaterial inserted in the cores, and particularly when the connectionmembers are made of metallic material. To overcome this difliculty, Iprovide each of the bushings as illustrated for the bushing Hb in Figs.4 and 5, with a slot lZa opening through the compressing face of thebushing and of substantially the thickness of the connection memberemployed, the slot extending transversely across the bushing andlongitudinally thereof. In the slot so, formed, I place a thin plate 22of suitable material, for example, hardened steel or steel alloy, inwhich, as more clearly shown in Figs. 6 and 7, a seat 22a has beenformed extending through the plate, said seat having a conformation tofit the edges of the portion of the connection member which is toproject from the core when the core-is completed, the form of the seat22a being such that the large pressures on the connection memberresulting from adhesion of the end portions of the connection memberwith the comminuted magnetic material during a compression operation,will all be exerted outwardly against the seat, so that the connectionmember will not buckle or be deformed as to its portion contained in thebushing, by the compressing operation. The plate 22 formed as described,is a snug fit in the slot Ma and is secured therein in any convenientmanner, for example by welding at its end portions. With some lands ofcomminuted material and particularly where heat is used in compressingthe cores, the compressed cores adhere to the compressing faces sostrongly that they cannot be safely removed from said compressing facesuntil they have cooled and hardened. Where the bushings carry connectionmembers as described, the adhesion between the ends of the bushings andthe ends of the compressed core, is large, particularly where heat isused in compressing the core, and the plunger bushings described,provide a means for cooling and hardening the compressed cores so thebushings may then be removed from the cores without injuring them..

4 being in the form of a staple, made by suitably bendinga rod or wireto the shape indicated.

The connection member 25 illustrated in Figs. and 11 is of sheetmaterial provided with an aperture 26a in the portion that projects fromthe finished core, the remaining portion of the connection member beingcontinuous and imperf rate and preferably having edges diverging fromeach other away from the aperture 26a.

The connection member 25 illustrated in Figs. 12 and 13 is of sheetmaterial having an aperture 25a in its projecting portion and a secondaperture 25b in its portion to be embedded in the material of the core,so that said material mayat least to some extent, enterthe-aperture 25band interlock with the connection member. The

connection member 26 illustrated in Figs. 14 and.

15 is of sheet material provided with an aperture 2M in its projectingportion relatively to the finished core, its other end portion beingprovided with slits 26b so that the resulting tongues of sheet materialmay be slightly bent in opposite directions, as illustrated in Fig. 15,to facilitate efiective interlocking with the material of the coreduring a compressing operation.

In Fig. 16, Iillustrate a finished core 2'5 in the end portions of whichthe adjacent endportions of connection members of the stapletypeillustrated in Figs. 8 and 9, have been embedded during the compressingoperation. As illustrated in this figure, the end portions Zlla and Ziaof the connection members 2d and 2 I, are shown as substantially bentfrom their original form, by the adhesion or friction of the endportions with the material of the compressed core during the compressingoperation, so that the connection members have'clinching engagement withthe core. At the same time, by supporting the connection members in theseats 22a above described, during of the core 28 to leave apertures 24ain the pro-- jecting portions of the connection members to receive theflexible operating cables to be employed. The connection members 25 arein part embedded in the end portions of the core 29 so that the materialof the core will interlock with the apertures 25b in said connectionmembers and leave the apertures 25a. in the projecting portions of theconnection members for attachment to' the flexible operating cables tobe employed.

In Fig. 19, I illustrate the core 29 in front elevation' to show thedeformation that may occur in the embedded portions of the connectionmembers bythe compressing operation, and by which to a greater or lesserdegree, clinching engagement between the connection member and the coreresults. The illustration in Fig. 19 also 11- lustrates in frontelevatloneither of the completed cores shown in Figs. 16 and 17.

In Fig. 20, I illustrate a completed core 30 provided with connectionmembers 26 having their split ends embedded in the core material andwith their apertures 26a. extending through the projecting portions ofthe connection members aaiaece for attachment with the flexibleoperating cables to be employed. 4

In Fig. 21, I illustrate the core 30 in Iront elevation to show thedeformation of the split end portions of the connection members 26 bythe compressing operation to effect clinching engagee ment between theconnection members and the I ing operation. It will further be observedthat regardless'of the type of connection member employed, said memberpresents an aperture for connection with the flexible cable that is ,tobe used to operate the core. It will be understood that the connectionmembers 29 may be of any wire or rod material that has the requisitestability and strength to secure the results above described, whethersaid material be non-metallic or metallic; in fact, I find that flexiblecord of fibrous material can be efiectively used to produce connectionmembers of this type, the flexible nature. of the material making itunimportant whether or not the projecting loop portion of the connectionmember is supported against deformation during the compressingoperation. Where the connection members are of sheet material, thematerial may either be non-metallic or metallic, the bnly requirementbeing that the material shall be as thin and of as small cross- 1section as the particular material will permit,

while at the same time affording the stability.

and strength requisite forthe purposes described. The importantconsiderations are that the connection members in any case shall beslender and of small cross-section so thateven with nonmetallic,connection members, made for example of Bakelite, the amount ofdisplaced magnetic material of the cores due to the embedded portions ofthe connection members, shall be a minimum, so that the magnetic actionof the cores when used with high frequency inductance coils shall besubstantially the same as though there were no disturbance whatever ofthe uniform distribution of the magnetic material of the core betweenlts ends. Where the connection member's are metallic, it is equallyimportant that they shall be slender and of small cross-section, bothfrom the standpoint of displacement of magnetic material in the coresand from the standpoint of presenting possible closedcircuit paths forthe flow of induced electric currents that might appreciably afiect theefliciency of operation of the cores.

When it is realized that the magnetic cores described are frequently assmall as in diameter, and that they may be required to be from 1 to 1long for that diameter, it will be better understood why the connectionmembers must be slender and of small cross-section to secure the resultsdescribed; again, in some cases. the cores may be required to be asshort as /3", which emphasizes the importance of having but a smallamount of embedment of the connection members in the cores. Where theconnectionmembers are of the type illustrated in Figs. 8 and 9 and areof metal, I find it desirable to use a. wire or rod not more than 3 indiameter and prefmysmaller; and where the connection members are of hetype illustrated in Figs. 10-15 inelusive and are of metal, I find itdesirable to makethem of sheet metal no thicker than 3 and preferablynot over thick.

Bythe term slender connection member or connection member of smallcross-section as used herein, I mean a member of such small diameter ifmade of wire, rods 'or the like, and of such small thickness if made ofsheet material, that if metallic, no appreciable lossesare added therebyto the operation of the cores at high frequencies, and in any event, ofwhatever material the connection member may be made, that the quantityor mass of the magnetic material of the core around the connectionmember, is not substantially reduced by the presence of the member fromwhat it would be without said member; furthermore, the connectionmembers contemliated by the present invention, have small lateralstability, being principally relied upon to withstand the axial strainsincident to moving the cores longitudinally for effecting inductancechanges as described above.

It will be imderstood that the compressed cores of the present inventionmay have any composition, any form of cross-section and any externalformjhat' may be adapted to and required by practical manufacture andthe purposes for which the'cores are intended. It will also beunderstood that although the, end connection members are shown in thedrawings as being in substantlally the same plane for each of theillustrated cores, the planes of said connection members for any of saidcores may have any angular relation to each other, unless the device orthe core operaflng mechanism with which the core is to be used, imposessome restriction in that connectim.

While the insert plates 22 above described, constitute a most effectivemeanstor providing the and plunger bushings with, supporting seatsfozr'the portions of the connection members projecting from the finishedcores, my invention alsoincludes plunger-s and plunger bushings of thekinds described, which are not prorider! with such plates 22, and whichhave suitable seats for said connection members formed in the materialof the u where and as such constructions may be prefen'ed.

While I have shown my invention in the particular embodiment abovedescribed, it will be understood that I do not limit myself thereto asthe scope of the appended claims. I

living thus described my invention, what I claim is: V

1. A magnetic core of compressed and insulated plungers and bushings,-

I may employ equivalents without departing from ferromagnetic particlesfor high frequency use and having an outer diameter of the order at mostof one-fourth of an inch, having molded in place in at least one of itsends a portion of a connection member having a thickness not more thansubstantially one-sixth of the outer diameter of the core and of frailmaterial readily deformable under light lateral pressure, thecross-section of said member being sufiiciently small so the quantity ofmagnetic core material in the core with the embedded portion of saidmember present is not substantially less than it would be with saidembedded portion absent from said core, and sufficiently small so noappreciable-losses are added to the core at high frequencies bytheconnection memben'said member comprising a metal wire having its endembedded in and having clinching engagement with said core material.

2. A magnetic core of compressed and insulated ferromagnetic particlesfor high frequency use and having an outer diameter .of the order atmost of one-fourth of an inch, having molded in place in at least one ofits ends a portion of a connection member having a thickness not morethan substantially one-sixth of the outer diam-- eter of the core and offrail material readily deformable under light lateral pressure, thecrosssection of said member being sumciently small so the quantity ofmagnetic core material in the core with the embedded portion of saidmember present is not substantially less than it would be .with saidembedded portion absent from said core, and sufliciently small so noappreciable losses are added tothe core at high frequencies by theconnection member, said member having a portion projecting from the corematerial for attachment purposes and having another portion fixedlyembedded in the material of the core.

3. A magnetic core of compressed and insulated ferromagnetic particlesfor high frequency use and having an outer diameter of the order at mostof one-fourth of an inch, having in at least one of its 'ends a portionof a connection member having a'thickness not more than substantiallyone-sixth of the outer diameter of the core and of frail materialreadily deformable under light lateral pressure, the cross-section ofsaid member being sufliciently small Sothe'quantity of magnetic corematerial in the core with the embedded portion of said member present isnot substantially less than it would bewith said embedded portion absentfrom said core, and sufficiently small so no appreciable losses areadded to the core at high frequencies by the connection member, saidmember havin a portion projecting from the core material for attachmentpurposes and having another portion fixed in the material of the core.

ALLEN D. WHIPPLE.

